In electrical machining of this type, which is also commonly called "wire-cut EDM" or "traveling-wire EDM", the wire electrode is continuously advanced from a supply side to a takeup side through a machining zone in which the workpiece is positioned and to which a machining liquid, typically distilled water or a liquid dielectric, is supplied. The workpiece is juxtaposed with the axially traveling wire across the machining zone between a pair of guide members which serve to stretch the traveling wire and to position it precisely in a predetermined machining relationship with the workpiece. A series of electrical pulses are applied across a machining gap formed between the workpiece and the traveling electrode to effect time-spaced electrical discharges thereat to electroerosively remove material from the workpiece. As material removal proceeds, the workpiece is displaced relatively and transversely to the continuously traveling wire electrode, typically under numerical control, along a predetermined path to generate a desired pattern of cut in the workpiece. The continuous advancement or travel of the wire is effected typically by traction drive rollers disposed at a location between the guide member on the downstream side and the wire take-up means. A desired tension is established in the traveling wire typically by providing brake rollers at a location between the guide member on the upstream side and the wire supply means.
As described in the aforementioned copending applications, the achievement of a satisfactory machining accuracy requires the use of a wire electrode as thin as 0.05 to 0.5 mm in diameter. This requirement has heretofore imposed restrictions in machining performance. Such a thin wire, given a desired tension, tends to be broken when arcing or short-circuiting with the workpiece takes place occasionally. Thus, the machining efficiency or removal rate hitherto achievable has been limited to an unsatisfactory level since wire breakage is unavoidable when an enhancement of machining efficiency or an increase in the rate of relative displacement is attempted.